The present invention relates to a driving apparatus and method of driving a driven member including a piezoelectric actuator using displacement elements such as piezoelectric elements or their equivalent.
Piezoelectric actuators that are widely known in the conventional art have a construction in which a prescribed displacement is caused in multiple piezoelectric elements based on prescribed drive signals output thereto to cause the tip member (the synthesizing member) connected to the tip end of each displacement element to perform a prescribed motion (for example, an elliptical motion), so that a prescribed member that is in frictional contact with the tip member is rotated or moved in a linear fashion.
One such driving apparatus including a piezoelectric actuator includes, as shown in FIG. 18, for example, a piezoelectric actuator 801 that has the construction described above and is located close to the driven member S, and a pressure mechanism 802 that keeps the driven member S and the piezoelectric actuator 801 in pressure contact such that a prescribed frictional force is generated on the contact surfaces of the tip member 801a of the piezoelectric actuator 801 and the driven member S.
This driving apparatus is constructed such that prescribed drive signals are output to the piezoelectric elements 801b while the tip member 801a is maintained in somewhat elastic pressure contact with the driven member S, in order to cause the tip member 801a to move in the direction indicated by the arrow TA, so that the driven member S is rotated in the direction indicated by the arrow TI around the rotational axis 803.
The base member 801c of the piezoelectric actuator 801 is fixed by a support member 804. This base member 801c is held by the pressure mechanism 802 such that it can move forward and backward (i.e., in the horizontal directions in FIG. 18), and is pressured forward by the spring member 802 of the pressure mechanism 802. Consequently, the piezoelectric actuator 801 is maintained in pressure contact with the driven member S. Even if the position of contact changes due to decentered rotation of the driven member S, such change is absorbed by the elasticity of the spring member 802.
Using the above construction, if a high output is desired, driving should be caused such that the piezoelectric actuator 801 resonates. Therefore, typically, the material and mass of each component are designed based on simulation of the oscillation of each component that comprises the piezoelectric actuator 801, such that the tip member 801a will move in a desired elliptical path with this resonance. The oscillation of the base member 801c is also taken into consideration.
However, the problem arises that when the base member 801c is fixed, as in the conventional driving apparatus, the oscillation of the base member 801c is hindered by the support member 804, and the desired elliptical locus cannot be obtained.
These and other drawbacks and deficiencies exist in conventional systems and methods.
The present invention was created to address the above problem, and provide a driving apparatus that reliably causes the tip member to perform a desired motion and improves the precision of drive control regarding the driven member.
One embodiment of the invention comprises a driving apparatus including: a driving unit having multiple displacement elements, a synthesizing member that is connected to the tip end of each displacement element and is in pressure contact with the driven member, and a base member that supports the base ends of said displacement elements; a spring member that is attached to said base member in order to press said synthesizing member onto said driven member; and a drive signal output unit that outputs drive signals to each displacement element to cause said synthesizing member to perform a specific motion, wherein said driven member is driven in a prescribed direction by having said synthesizing member perform a specific motion in accordance with the drive signals output from said drive signal output unit, and wherein regulating members that regulate the displacement of said driving unit itself, which is caused by the driving carried out by said driving unit, are located at positions that face said base member and are opposite from said driven member, at a prescribed distance from said base member.
In one aspect of this embodiment, regulating members that regulate the displacement of the driving unit itself that is caused by the driving carried out thereby are located at positions facing the base member and opposite from the driven member, and at a prescribed distance from the base member, and therefore the driving unit and the regulating members are not in contact. Consequently, hindrance of the oscillation of the base member by the regulating members is prevented, and motion in accordance with the drive signals output from the drive signal output unit may be reliably performed by the synthesizing unit.
In another aspect of this embodiment, the prescribed distance should equal or exceed the amplitude of the oscillation of the driving unit that is generated by the displacement of the piezoelectric elements.
In another aspect of this embodiment, the prescribed distance can equal or exceed the sum of the amplitude of the oscillation of the driving unit that is generated by the displacement of the piezoelectric elements and the length that accommodates the change in the contact position of the driven member.
In this embodiment, even where the operation of the driving unit is stopped, the driven member continues to move in the same direction in which it has been driven for some while due to the inertia that works on the driven member, and the synthesizing unit that is in contact with the driven member follows the movement thereof. If the construction is such that the spring member applies pressure to the driven member only in the direction perpendicular to the contact surfaces of the driven member and the synthesizing unit, the spring member elastically deforms in a direction other than this perpendicular direction (hereinafter any direction other than the perpendicular direction will be referred to as xe2x80x98a second directionxe2x80x99) due to the force (hereinafter the xe2x80x98following forcexe2x80x99) of the driven member that causes the synthesizing unit to follow its movement. When this following force becomes smaller than the restoring force that works in a second direction of the spring member, the synthesizing unit that followed the movement of the driven member begins to return toward the initial position prior to the driving of the driven member due to its restoring force, and conversely, the driven member begins to follow the movement of the synthesizing unit. When this occurs, based on the size of the restoring force, the synthesizing unit may come to a stop without returning to the initial position, or may pass the initial position before it comes to a stop. In other words, variations may occur in the position at which the driven member stops. In addition, the return of the synthesizing unit to the initial position translates into a loss of time insofar as speedy cessation of the movement of the driven member is concerned.
In another aspect of this embodiment, if the construction is such that the spring member exerts pressure in the direction perpendicular to the contact surfaces of the synthesizing unit and the driven member, and applies pressure to the driving unit such that it is maintained by the regulating members at a position that is upstream in terms of the direction of driving, even when the force of the driven member that causes the synthesizing unit to follow the movement thereof falls below the restoring force of the pressure unit, the driving unit is maintained by the regulating members at a position that is upstream in terms of the direction of driving, and the driving unit does not return to the initial position. Therefore, unlike in the example described above, no variations occur in the position at which the driven member stops, and as a result, the driven member is stopped with more precise control, the above time loss is eliminated, and less time is required for control to stop the driven member.
In another aspect of this embodiment, the driving unit can be supported such that it can rotate around a support member belonging to the regulating member.